A pole-mounted subscriber carrier referred to as an
Anaconda carrier.
In telephony, pair gain is a method of transmitting multiple POTS signals over the twisted pairs traditionally used
for a single traditional subscriber line in telephone
systems. Pair gain has the effect of creating additional subscriber lines. This is typically used as an expedient way to solve
subscriber line shortage problems by using existing wiring, instead of installing new wires from the central office to the customer premises. The term was invented in the middle 20th century by analogy
with earlier use of gain to extend telephone local loops far from the telephone exchange.
A pair gain system consists of concentrators or multiplexers which combine the separate signals into a single signal which is transmitted through the
existing copper cable pair. The signals are then separated into individual subscriber lines at the customer premises. The pair
gain unit which performs the multiplexing can be as simple as providing two telephone connections over a single subscriber
line (called an Analog Multi-Line Carrier or AML) in circumstances where a customer wants to add a new phone line for a
fax machine or dial-up internet connection. A larger analog
pair gain system made by Anaconda in the 1960s provided seven lines. Some pair gain units can expand the number of subscriber
lines available over a single copper pair to as many as sixty. Large pair gain units are stored in Serving area interfaces or metal cabinets typically resembling
small apartment-sized refrigerators alongside or near roadways that overlie communications
rights-of-way.
DACS (Digital Access Carrier System) was a form of pair gain used in
the United Kingdom. It uses a form of time division multiple
access called ISDN.
Analog pair gain has come into disfavor in recent years, as it is detrimental to high speed dial-up modem connections, does
not support 56k and is incompatible with Digital
Subscriber Line (DSL) systems. More recent digital pair gain systems take the concept even further, however, restoring 56k
and DSL capabilities by performing the functions of a DSLAM
at the pair gain device.
More recently, the term pair gain has been used to refer to any multiplex/demultiplex unit used between the
central office and end users, not just equipment used with copper.
See also
This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)
